1. Field of the Invention
This invention relates to the field of data formatting, and more particularly to the formatting of variable bit length data words into successive fixed bit length data words.
2. Description of the Prior Art
Some data compression systems produce compressed data comprising successive variable bit length code words. For example, in an image data compression system proposed by the Joint Photographic Experts Group (JPEG), image data are subjected to frequency separation, quantisation and then entropy encoding. The entropy encoding stage generates variable bit length data words in such a way that more commonly occurring data patterns (such as runs of zero-valued data) are encoded as shorter data words.
Although variable length encoding can allow data to be efficiently compressed, subsequent storage of the data or other processes such as error correction encoding generally operate on fixed length data words. It is therefore necessary to convert the variable length data words into fixed length data words. However, the data format conversion itself introduces an additional data processing overhead. In a non real time system, such as still image processing and display in a computer system, this is not a particular problem. However, in a system dealing with data such as real time video data, the high data rates present a particular challenge in providing data format conversion in a way that can keep pace with the overall data rate and only introduce a small time lag in the processing.